Display device for rotary balancing machines

ABSTRACT

The invention provides a display device for a rotary balancing machine. The balancing machine generates a digital out of balance weight signal of value W at an angular position θ with respect to a datum angle to indicate value and position of a weight required for balancing purposes. In the display device the weight signal is fed to a pre-programmable read only memory programmed to provide a digital output equivalent to an angle of arc cos ( W/2W 1 ) where W 1  is a predetermined weight to be used for balancing purposes. Angles θ 1  and θ 2  such that Δθ=θ-θ 1  =θ 2  -θ are normally displayed but for calibration purposes can be suppressed to enable signals W and θ to be displayed. Weights of the predetermined value placed at angles θ 1  and θ 2  should completely balance the wheel.

BACKGROUND OF THE INVENTION

The invention relates to display devices for rotary balancing machines.

It is already known for example from U.K. patent specification No.1,339,724 and the corresponding U.S. Pat. No. 3,732,737 to provide arotary balancing machine which provides a digital output in the form ofone value representative of the balance weight value required to balancea work piece and another digital value indicative of the angularposition with respect to a datum at which the weight should be placed.In a wheel balancer for balancing automotive and similar wheels, it isdesirable to balance the wheel in two planes to ensure that out ofbalance couples as well as out of balance forces are taken intoconsideration when balancing the wheel. The axial positions (that isradial planes) at which weights can be added are defined by thestructure of the wheel so that in the case of a wheel balancer, what isrequired and available from the known balancers is a weight value and anangular position value for each of the two planes.

Considering for the moment only the situation within a single radialplane, it has been proposed in U.S. Pat. No. 3,550,455 that in order tostandardise the value of weights which have to be made available, a pairof weights of a predetermined standard value may be employed at angularpositions to either side of the nominal position at which a singleweight would be placed.

In further detail, when:

W is the value of a single weight required to balance a wheel θ is theangle with respect to a datum at which weight W should be placed.

W₁ is the value of standardised weight

θ₁ and θ₂ are angles with respect to the datum at which weights W₁should be placed to be equivalent of weight W at angle θ.

Δθ is equal to θ-θ₁ and equal to θ₂ -θ

Then:

    θ=arc cos (W/2W.sub.1)

It has also been proposed in U.S. Pat. No. 4,068,532 to provide anelectronic arithmetic unit to calculate from weight and basic anglesignals the corresponding angle positions for weights of a single weightvalue to replace the single weight at the basic angular position.

The present invention is concerned with certain details of a displaydevice for a rotary balancing machine which display device includesmeans for receiving signals indicative of values of W and θ, means forcalculating corresponding values of θ₁ and θ₂ for weights ofpredetermined value W₁ and means for displaying in digital form theangles θ₁ and θ₂.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided adisplay device for a rotary balancing machine which machine is of thekind which generates a digital out of balance weight signal of valuedefined as W and a digital out of balance position signal of angledefined as θ with respect to a datum angle to give an indication of thevalue and position of a weight required for balancing purposes and inwhich balancing requirements are to be converted to digital positionvalues for weights of predetermined uniform value defined as W₁, whereinto calculate the angle defined as Δθ in relation to weight position θ atwhich weights of value W₁ should be placed to give a resultant balancingeffect equivalent to W at θ, the signal indicative of weight W is fed toa pre-programmable read only memory device (hereinafter PROM) programmedto give a digital output Δθ equivalent to an angle of arc COS (W/2W₁),provided W/2W₁ <1, to indicate a requirement for weights of value W₁ atangles θ₁ and θ₂ defined by: θ₁ =θ-Δθ and θ₂ =θ+Δθ.

Preferably the PROM is programmed so that when W/2W₁ =1, then θ₁ and θ₂are each approximately equal to θ. For practical convenience it ispreferred to specify small angles either side of θ to provide for thefinite length of the weight.

Preferably the PROM is programmed so that when W/3W₁ <1 <W/2W₁ it givesan output signal of arc COS (W-W₁)/2W₁ together with an indication thata third weight is required at angle θ. The value of this third weight isof course W₁.

Preferably the PROM is programmed so that when W/3W₁ >1, it gives anoutput signal of θ and suppresses θ₁ and θ₂, indicating a requirementfor some weight at angle θ. It is convenient to use a weight of theorder of 3W₁, but this is not critical. This weight addition reduces theout of balance so that balance can be achieved in a subsequent balancingoperation.

According to a second aspect of the invention there is provided adisplay device for a rotary balancing machine which is of the kind whichgenerates a digital out of balance weight signal of value defined as Wand digital out of balance angular position signal of angle defined as θwith respect to a datum angle to give an indication of the value andposition of a weight required for balancing purposes includingcalculating means for calculating in digital form angular positionsignals defined as θ₁, θ₂ indicative of angles at which weights of apredetermined uniform value should be placed to be equivalent to weightW at angle θ, digital display means for displaying said angular positionsignals θ₁, θ₂ and means for suppressing said angular position signalsθ₁, θ₂ and displaying weight and angular position signals W and θ insaid display means to operate said display device in a calibration modefor calibrating the balancing machine.

A typical balancing machine is such that the relationship between ananalogue out of balance force signal and the actual out of balanceweight of a work piece is a linear relationship but the actualconvertion factor cannot be predetermined and has to be set by adjustingthe gain of an amplifier on installation of the machine. The mostconvenient way to do this is to operate the machine with a test pieceincorporating a known out of balance force at a known angle, reading therecorded out of balance weight on a display device and adjusting thegain of the amplifier so that the displayed value corresponds to theactual out of balance weight of the test piece. At the same time, theangle indicating function of the machine can be checked if the out ofbalance angle is also displayed and corresponds to the out of balanceangle of the test piece.

It is inconvenient and inaccurate to use for calibration purposes thedisplay in the form of angle signals for weights of pre-determinedvalue, partly because approximation is required in converting weightsignals to angle signals and partly because during calibration it isdesirable to use large out of balance weight values which are notparticularly easily dealt with by an angle only display system.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will now be described by way of exampleonly with reference to the accompanying circuit diagram and table 1which indicates the relationships between various binary signals.

Input Signals

The inputs to the display device are shown at the left hand side of thedrawing. The weight input signals are received at terminals WA₀ to WA₅respectively. The weight signal is given to the nearest 5 grams andterminal WA₀ is used to indicate whether the units figure of the weightvalue is 0 or 5. Terminals WA₁ to WA₄ are used to receive the tensfigure in binary coded decimal form. The maximum out of balance weightwhich can be measured is 195 grms, so a single terminal WA₅ is needed toindicate whether the hundreds figure should be 0 or 1.

The angle signal θ is provided in decimal form in units of 5° tocorrespond to 72 specific angular locations defined in the machine.Units value of the angle is indicated in binary coded decimal (BCD) formon inputs UA UB UC and UD. Similarly, the tens figure for the angularposition is indicated in BCD form at inputs TA TB TC and TD.

A control input C is also provided to control the time at which theinput signals cause the display device to respond.

These input signals may be derived from a rotary balancing machine asdescribed in my U.S. Pat. No. 3,732,737 the disclosure of which isincorporated herein by reference.

Angle Calculation

The weight input signals are fed directly or indirectly through OR gatesG₁ and G₂ to a programmable read only memory PROM which is programmed asindicated in table 1 to convert the input weight signal to angle signalswith respect to the basic single weight angle θ. The display system isintended to indicate a requirement for a maximum of 3 weights of 30 grmseach at the same location, in other words for a maximum weight of 90grms to be added. For this reason, it is unnecessary to provide aseparate input to the PROM for the hundreds signal but instead thehundreds signal is gated to two inputs of the tens BCD to ensure thatwhen the actual weight is in the hundreds, the weight signal fed to thePROM is at least 90 grms.

The relationship between the input weight signals WA₀ to WA₅, PROM inputsignals A₀ to A₄ and PROM output signals B₀ to B₇ is indicated in thetable. It can be seen that on all occasions when the weight W exceeds 90grms the signals at A₃ and A₄ are `1`s so that the total PROM inputsignal is at least binary 11000, in other words at least 120 grms.

The PROM is programmed so that whenever the inputs are in the form ofcolumn A of the table, the outputs are in the form of column B of thetable. These outputs indicate the required angle Δθ but also show otherfunctions. Outputs B₀ to B₃ give the unit figure for Δθ in BCD. OutputB₄ gives the tens figure for Δθ which is either 1 or 0 in decimal termsbecause the maximum value for Δθ is 18 units of 5° per unit. Output B₅indicates whether or not θ should be suppressed or displayed at thedisplay in a display unit intended for use when a third weight W₁ isrequired, that is when W exceeds 60 grms. Output B₆ is used to indicatewhen a balanced condition exists. A balance weight requirement of lessthan 10 grms is considered to be sufficient for there to be norequirement to add weights. Output B₇ is used to indicate that W isgreater than 90 grms so that the addition of weights does not result inbalance.

Display of θ₂

The BCD inputs UA to UD and TA to TD are fed respectively to decadecounters C₁ and C₂ to set these counters to the value of θ. The unitscounter C₂ can be counted up from an input 11 which receives a train ofpulses corresponding to Δθ in a way which will now be explained.

Returning to the output of the PROM, and particularly outputs B₀ to B₄inclusive, these are fed to two decade counters C₃ and C₄ respectivelyand are set to Δθ. Outputs from the counters C₃ and C₄ are connectedthrough a network of NOR gates G₃ and G₄ and NAND gate G₅ to clock pulseNAND gate G₆ which controls the output of clock pulses from a clockpulse generator CP. The output train of clock pulses is connected bothto the counter C₂ at input 11 and to counter C₄ at input 12. Counters C₁and C₂ are connected in cascade by connections 13 and 14 and counters C₃and C₄ are similarly connected in cascade by connections 15 and 16. Thusthe counters C₃ and C₄ together are counted down in sequence withcorresponding counting up of counters C₁ and C₂. This counting continuesuntil all the outputs from counters C₃ and C₄ are in the 0 state,meaning that the cascade of counters C₃ and C₄ has been counted to 0 andat that stage a signal passes through the network of gates G₃ G₄ and G₅to an input of NAND gate G₆ so that it cuts off further clock pulses. Inthis way, counters C₁ and C₂ are counted up by the original count ofcounters C₃ and C₄ so that the total count of counters C₁ and C₂ becomesequal to the count of θ plus the count of Δθ. This count isrepresentative of θ₂ because θ₂ equals θ plus Δθ.

In order to cater for the situation when θ plus Δθ is greater than 71 sothat θ₂ should be displayed as θ plus Δθ minus 72, the cascadeconnection of counters C₁ and C₂ includes a loop with NAND gates G₇ andG₈ to reset the counter to 0 when the output reaches 72.

The outputs from counters C₁ and C₂ are connected to decoders D₁ and D₂which are in turn connected to conventional seven segment display unitsDIS₁ and DIS₂. Output from the decoders is normally inhibited until thecounting operation has been completed through connections 17 and 18 ofthe decoders D₁ and D₂, the sources of which will be describedsubsequently but when the final value of θ₂ has been calculated asdescribed above, the inhibition is cancelled so that θ₂ is displayed inthe display units DIS₁ and DIS₂.

Display of θ₁

θ₁ is calculated and displayed in a way which is generally similar tothe calculation and display of θ₂. A first difference is associated witha possible counting down through 0 after which the next down countshould be 71. The value of θ is fed from inputs UA to UD and TA to TD totwo two-way multiplexer devices G₉ and G₁₀ which are set to θ inresponse to a load command signal which will be described subsequentlyand which at all other times are set to 71. The outputs from thesetwo-way multiplexers G₉ and G₁₀ are connected to two decade counters C₅and C₆ so that these can be set to θ. Counters C₅ and C₆ can be counteddown by the gated clock pulses from gate G₆ in exactly the same way ascounters C₁ and C₂ were counted up. At the termination of the countingoperation, the count stored in counters C₅ and C₆ then amounts to θ-Δθ,that is θ₁.

In counting down, the count required immediately after 0 is not 99 butis 71. This is because a complete circle of angular movement isconstituted by 72 divisions of 5° each. To achieve this count of 71, anoutput of 99 is detected by NAND gates G₁₁ and G₁₂ which signal thecounters C₅ and C₆ via OR gate G₁₃ and one shot TD to reset the countersto the value contained in multiplexers G₉ and G₁₀ that is the value 71.

The output from the counters C₅ and C₆ is then normally passed throughtwo-way multiplexers G₁₅ and G₁₆ to decoders D₃ and D₄. A displayenabling signal is applied to inputs 19 and 20 of the decoder when thecounting has been completed so that the θ₁ signal stored in counters C₅and C₆ can be displayed in display units DIS₃ and DIS₄.

The other inputs which can be fed to the θ₁ display units DIS₃ and DIS₄via multiplexers G₁₅ and G₁₆ will be described subsequently in relationto the calibration mode of the complete system.

Display of θ

The signals representative of θ at inputs UA to UD and TA to TD are alsofed directly to decoders D₅ and D₆ which in turn are connected todisplay units DIS₅ and DIS₆.

As described above in relation to the PROM device, no weight is to beplaced at angle θ when the total out of balance is less than 60 grms butan output display of θ is required when Δθ is greater than 60 grms. Anappropriate display enabling signal derived in a way to be describedsubsequently is applied to inputs 21 and 22 of decoders D₅ and D₆ toenable θ to be displayed in display units DIS₅ and DIS₆.

Display Enabling Signals

The normal display enabling requirements are that no output should bedisplayed either when the balancer is running up to speed or while thecounting calculations are taking place. Once the balancer has reachedits appropriate speed and the calculations have been completed, theappropriate information should be displayed and should continue to bedisplayed until either the machine is switched off or a new balancingoperation is commenced. An external display enabling signal is appliedto input C.

The display enabling signal at input C is a 0 and this signal is feddirectly to NOR gate G₁₇ and from there is fed directly to displayenabling input 17 and through OR gates G₁₈ and G₁₉ to display enablinginputs 18, 19 and 20. Thus θ₁ and θ₂ are normally displayed in responseto a 0 on input C.

Output B₇ from the PROM device is connected to gate G₁₇ to inhibitdisplay of θ₁ or θ₂ when the weight W exceeds 90 grms.

The 0 signal from input C is also supplied through a NOR gate G₂₀ and ORgate G₂₁ to display enabling inputs 21 and 22 of decoders D₅ and D₆ toenable θ to be displayed in display units DIS₅ and DIS₆. When W isbetween 0 and 60 grms an inhibit signal from output B₅ of the PROMdevice is fed to gate G₂₀ to inhibit passage of the display signalthrough that gate and therefore to prevent display of θ.

Display of Balanced Condition

When the out of balance weight is less than 10 grms no addition ofweights to a wheel is required and the display of θ₁ θ₂ and θ isinhibited. The inhibit signal is derived from output B₆ of the PROMdevice which is connected to gate G₁₇ to inhibit the display enablingsignal from this gate to decoders D₁ D₂ D₃ and D₄. With such a lowweight, display of θ is automatically inhibited as previously described.A display enabling signal from output B₆ reaches decoder D₂ through asecond input of gate G₁₈. Output B₆ is also connected to terminal 23 ofdecoder D₂ to cause the decoder to illuminate all 7 display elements andthus exhibit an 8 which in this situation is intended to be read as a B.Output B₆ also activates a power source P which provides power to a busrail BAL which is in turn connected directly to 3 appropriate elementsof display device DIS₄ and 6 appropriate elements of display device DIS₆so that these display devices display an A and L respectively. In thedisplay equipment, display units DIS₂ DIS₄ DIS₆ are arranged in line sothat the complete display has the form BAL indicative of balance of thewheel.

Operation in the Calibration Mode

In the calibration mode, a calibration circuit CC is rendered operativeby closing calibration switch CS so that a 1 signal is developed atoutput CC₁ and a 0 signal (as opposed to a previous 1 signal) at outputCC₀. The signal from CC₁ is supplied to the two-way multiplexers G₁₅ andG₁₆ to switch these gates over from counters C₅ and C₆ to inputs WA₀ toWA₄ respectively. This causes the display devices DIS₃ and DIS₄ todisplay the out of balance weight in grms instead of displaying θ₁. Asout of balance weights used during calibration are less than 100 grms,there is no requirement for displaying the 100's element of weight Wfrom input WA₅. An output from CC₁ is also fed to gate G₂₁ to provide anenabling signal at inputs 21 and 22 of decoders D₅ and D₆ so that θ isdisplayed in display devices DIS₅ and DIS₆ . Output CC₀ from thecalibration circuit CC is connected to the power source P to inhibitsupply of power to the bus rail BAL and thus inhibit the A and the L ofthe normal balance signal. However, in order to enable balance still tobe indicated during operation in the calibration mode, the possibledisplay of a B in display unit DIS₂ when the out of balance weight isless than 10 grms is not inhibited. Because greater accuracy is requiredduring calibration than in normal operation, the actual out of balanceweight W is displayed in display units DIS₃ and DIS₄ even when nominalbalance is indicated.

Loading and Re-Setting of the Complete System

It is necessary to ensure that the counters C₁ to C₆ respectively do notbecome connected to their inputs until stable signals have beenachieved. It is also necessary to ensure that they do not remainconnected to their inputs after the beginning of the counting operation.For this reason a load signal of short duration is required shortlyafter the appearance of the display signal at control input C. For thisreason input C is connected through a delay device DD to a one shot PGwhich generates a load command signal pulse at output L shortly afterthe display signal occurs at the control input C. This load signal issupplied to counters C₁, C₂, C₃ and C₄ directly and to multiplexers G₉and G₁₀ for counters C₅ and C₆ so that the counters are loaded. The loadsignal is also supplied to gate G₆, which controls the countingoperation and inhibits the supply of clock pulses for a sufficient timeto ensure that the counters are loaded correctly.

General Operation

In operation of the wheel balancer, a wheel is mounted on the spindle ofthe machine and is spun up to speed in order to generate the W and θsignals. If the display device indicates that the wheel is balanced, noaction is necessary. If on the other hand, there is an out of balancebetween 10 and 60 grms, θ₁ and θ₂ are displayed as appropriate valuesfor addition of 30 grm weights to correct the out of balance. If the outof balance weight is between 65 and 90 grms, θ, θ₁ and θ₂ are alldisplayed to indicate a requirement for weight at the 3 locations toachieve balance. If the out of balance weight is greater than 90 grms,and there is no specific upper limit to the out of balance weight whichcan be catered for, a weight should be added at position θ. If the onlyweights available are 30 grm weights, it is desirable to add 2 of theseat position θ, but it is preferable to use single weight of about 60 to90 grms if this is available. The actual value of this weight isunimportant. When the new weight has been added, a new balancingoperation is carried out and it is to be hoped that with the previousaddition of 60 grms or so, the remaining out of balance should be lessthan 90 grms so that complete balance can be achieved with two or threeadditional 30 grm weights. In the extremely unusual situation where aweight of approximately 60 grms does not bring the wheel within 90 grmsof balance, the display device will again illuminate only the angle θ,indicating that further weight should be applied to this position beforecarrying out a further balancing operation. If necessary, this operationcan be completed an indefinite number of times until balance isachieved.

As a check on the correct positioning of weights, it is alwaysrecommended that when weights have been added, a further balancingoperation should be carried out as a check to ensure that balance hasbeen brought within the 10 grm limit set by the machine.

Balancing in two Planes

As thus far described, the display device operates solely to displaybalancing requirements in one plane of a wheel. In the case of abalancer intended to balance couples as well as out of balance forces, asecond complete device corresponding to that described above should beprovided to enable the requirements for balancing in the other plane tobe displayed. As an alternative, switching means could be provided forswitching the system described between input data for two planes andeach plane could be balanced in turn.

General

Although the detailed description has for convenience made reference toweights of 30 grms, the balancing machine could be calibrated in such away that the input weight signals represent other weights besides 5 grmsper unit in which case a different standard weight should be used.Alternatively, the PROM device could be re-programmed to cater forweights other than 30 grms.

Although the detailed description of the invention has for conveniencemade reference to its use in connection with a wheel balancer, theinvention is not so limited and could be used in connection with anyrotary balancing machine which provides a suitable digital output.

                                      TABLE 1                                     __________________________________________________________________________    WA                A          B                                                Weight                                                                             5 4 3 2  1 0 4 3 2  1 0 7 6 5 4 3 2 1 0 .increment.0                     __________________________________________________________________________     0   0 0 0 0  0 0 0 0 0 0  0 0 1 1 1 1 0 0 0 18                                5   0 0 0 0  0 1 0 0 0 0  1 0 1 1 1 0 1 1    1                                                                        17                                   10   0 0 0 0  1 0 0 0 0 1  0 0 0 1 1 0 1 1    0                                                                        16                                   15   0 0 0 0  1 1 0 0 0 1  1 0 0 1 1 0 1 0    1                                                                        15                                   20   0 0 0 1  0 0 0 0 1 0  0 0 0 1 1 0 1 0    0                                                                        14                                   25   0 0 0 1  0 1 0 0 1 0  1 0 0 1 1 0 0 1    1                                                                        13                                   30   0 0 0 1  1 0 0 0 1 1  0 0 0 1 1 0 0 1    0                                                                        12                                   35   0 0 0 1  1 1 0 0 1 1  1 0 0 1 1 0 0 0    1                                                                        11                                   40   0 0 1 0  0 0 0 1 0 0  0 0 0 1 1 0 0 0    0                                                                        10                                   45   0 0 1 0  0 1 0 1 0 0  1 0 0 1 0 1 0 0    0                                                                        8                                    50   0 0 1 0  1 0 0 1 0 1  0 0 0 1 0 0 1 1    1                                                                        7                                    55   0 0 1 0  1 1 0 1 0 1  1 0 0 1 0 0 1 0    1                                                                        5                                    60   0 0 1 1  0 0 0 1 1 0  0 0 0 1 0 0 0 1    0                                                                        2                                    65   0 0 1 1  0 1 0 1 1 0  1 0 0 0 1 0 0 0    1                                                                        11                                   70   0 0 1 1  1 0 0 1 1 1  0 0 0 0 1 0 0 0    0                                                                        10                                   75   0 0 1 1  1 1 0 1 1 1  1 0 0 0 0 1 0 0    0                                                                        8                                    80   0 1 0 0  0 0 1 0 0 0  0 0 0 0 0 0 1 1    1                                                                        7                                    85   0 1 0 0  0 1 1 0 0 0  1 0 0 0 0 0 1 0    1                                                                        5                                    90   0 1 0 0  1 0 1 0 0 1  0 0 0 0 0 0 0 1    0                                                                        2                                    95   0 1 0 0  1 1 1 0 0 1  1 1 0 0 0 0 0 0    0                                                                        0                                     95+ 1 ←                                                                          ←                                                                          any                                                                              →                                                                        →                                                                        1 1 ←                                                                          any                                                                              →                                                                        1 0 0 0 0 0 0    0                                                                        0                                             ↓     ↓     ↓                                   .BHorizBrace.     .BHorizBrace.                                                                            .BHorizBrace.                                    __________________________________________________________________________

I claim:
 1. In a rotary balancing machine of the kind which generates adigital out of balance weight signal of a value defined as W and adigital out of balance position signal of angle defined as θ withrespect to a datum angle to give an indication of the value and positionof a weight required for balancing purposes, a display device forindicating digital position values at which weights of predetermineduniform value defined as W₁ should be placed to give a resultantbalancing effect equivalent to weight W at θ, the display devicecomprising:a pre-programmable read only memory arranged to receive saidweight signal, said memory being pre-programmed to provide a digitaloutput Δθ equivalent to an angle arc COS (W/2W₁) when W is in the rangesuch that W/2W₁ <1, the pre-programmable read only memory also beingpre-programmed to provide other digital outputs in response to specificvalues of W when W is outside the range such that W/2W₁ is less than 1whereby requirements for achieving balance can be indicated when W isoutside the range of W/2W₁ <1. first means for receiving the positionsignal value θ, means for subtracting the value Δθ from the value θ toprovide a digital value defined as θ₁, second means for receiving theposition signal value θ, means for adding the value Δθ to the value θ toprovide a digital value defined as θ₂, and means for displaying thevalues of θ₁, and θ₂ to provide said digital position signals forweights W₁.
 2. In a rotary balancing machine of the kind which generatesa digital out of balance weight signal of a value defined as W and adigital out of balance position signal of angle defined as θ withrespect to a datum angle to give an indication of the value and positionof a weight required for balancing purposes, a display device forindicating digital position values θ₁ and θ₂ at which weights ofpredetermined uniform value defined as W₁ should be placed to give aresultant balancing effect equivalent to W at θ, digital calculatingmeans for deriving θ₁ and θ₂ such that θ₁ =θ-Δθ and θ₂ =θ+Δθ whereΔθ=arc COS (W/2W₁), means for displaying the values of θ₁ and θ₂ toprovide said digital position signals for weights W₁ and means forsuppressing the angular position signals θ₁ and θ₂ and displaying weightand angular position signals W and θ in said display means to operatesaid rotary balancing machine in a calibration mode for calibrating themachine.
 3. In a rotary balancing machine of the kind which generates adigital out of balance weight signal of a value defined as W and adigital out of balance position signal of angle defined as θ withrespect to a datum angle to give an indication of the value and positionof a weight required for balancing purposes, a display device forindicating digital position values at which weights of predetermineduniform value defined as W₁ should be placed to give a resultantbalancing effect equivalent to weight W at θ, the display devicecomprising;a pre-programmable read only memory arranged to receive saidweight signal, said memory being pre-programmed to provide a digitaloutput Δθ equivalent to an angle arc COS (W/2W₁) when W is in the rangesuch that W/2W₁ <1, first means for-receiving the position signal valueθ, means for subtracting the value Δθ from the value θ to provide adigital value defined as θ₁, second means for receiving the positionsignal value θ, means for adding the value Δθ to the value θ to providea digital value defined as θ₂, and means for displaying the values of θ₁and θ₂ to provide said digital position signals for weights W₁, whereinthe pre-programmable read only memory is so programmed that when W/2W₁=1 then Δθ is given as a small angle such that θ₁ and θ₂ areapproximately equal to θ but are spaced a finite distance to enable theapplication of two independent weights of value W₁.
 4. In a rotarybalancing machine of the kind which generates a digital out of balanceweight signal of a value defined as W and a digital out of balanceposition signal of angle defined as θ with respect to a datum angle togive an indication of the value and position of a weight required forbalancing purposes, a display device for indicating digital positionvalues at which weights of predetermined uniform value defined as W₁should be placed to give a resultant balancing effect equivalent toweight W at θ, the display device comprising;a pre-programmable readonly memory arranged to receive said weight signal, said memory beingpre-programmed to provide a digital output Δθ equivalent to an angle arcCOS (W/2W₁) when W is in the range such that W/2W₁ <1, first means forreceiving the position signal value θ, means for subtracting the valueΔθ from the value θ to provide a digital value defined as θ₁, secondmeans for receiving the position signal value θ, means for adding thevalue Δθ to the value θ to provide a digital value defined as θ₂, andmeans for displaying the values of θ₁ and θ₂ to provide said digitalposition signals for weights W₁, said pre-programmable read only memoryhaving a further output and being so programmed that when W/3W₁ >1 asignal is provided on the further output but no signal is provided foroutputs θ₁ and θ₂, the balancing machine further comprising third meansfor receiving the position signal value θ and means for displaying thevalue of θ in response to said signal on said further output of thepre-programmable read only memory.
 5. In a rotary balancing machine ofthe kind which generates a digital out of balance weight signal of avalue defined as W and a digital out of balance position signal of angledefined as θ with respect to a datum angle to give an indication of thevalue and position of a weight required for balancing purposes, adisplay device for indicating digital position values at which weightsof predetermined uniform value defined as W₁ should be placed to give aresultant balancing effect equivalent to weight W at θ, the displaydevice comprising;a pre-programmable read only memory arranged toreceive said weight signal, said memory being pre-programmed to providea digital output Δθ equivalent to an angle arc COS (W/2W₁) when W is inthe range such that W/2W₁ <1, first means for receiving the positionsignal value θ, means for subtracting the value Δθ from the value θ toprovide a digital value defined as θ₁, second means for receiving theposition signal value θ, means for adding the value Δθ to the value θ toprovide a digital value defined as θ₂, and means for displaying thevalues of θ₁ and θ₂ to provide said digital position signals for weightsW₁, said first means for receiving the position signal value θ being afirst counter, said means for subtracting the value Δθ being a furthercounter operatively connected to the pre-programmable read only memoryto receive the value Δθ, the rotary balancing machine also comprising acounting pulse generator and gating means for gating counting pulses tosaid counters for counting both counters down, and means operativelyconnected to the gating means to cut off the supply of counting pulseswhen said further counter has been counted down to zero.
 6. In a rotarybalancing machine of the kind which generates a digital out of balanceweight signal of a value defined as W and a digital out of balanceposition signal of angle defined as θ with respect to a datum angle togive an indication of the value and position of a weight required forbalancing purposes, a display device for indicating digital positionvalues at which weights of predetermined uniform value defined as W₁should be placed to give a resultant balancing effect equivalent toweight W at θ, the display device comprising;a pre-programmable readonly memory arranged to receive said weight signal, said memory beingpre-programmed to provide a digital output Δθ equivalent to an angle arcCOS (W/2W₁) when W is in the range such that W/2W₁ <1, first means forreceiving the position signal value θ, means for subtracting the valueΔθ from the value θ to provide a digital value defined as θ₁, secondmeans for receiving the position signal value θ, means for adding thevalue Δθ to the value θ to provide a digital value defined as θ₂, andmeans for displaying the values of θ, and θ₂ to provide said digitalposition signals for weights W₁, said second means for receiving theposition signal value θ being a second counter, said means for addingthe value Δθ being a further counter operatively connected to thepre-programmable read only memory to receive the value Δθ, the rotarybalancing machine also comprising a counting pulse generator and gatingmeans for gating counting pulses to said counters for counting thesecond counter up and the further counters down, and means operativelyconnected to the gating means to cut off the supply of counting pulseswhen said further counter has been counted down to zero.